1. Field of the Invention
The present invention relates to a liquid display device, and particularly, to a backlight unit and a liquid crystal display device having the same that minimize image quality degradation when light emitting devices are employed as a backlight lamp in the liquid crystal display device.
2. Background of the Invention
Various portable electronic devices, such as mobile phones, personal digital assistants (PDA), notebook computers, etc., have been continuously developed. As such, there is a demand in developing flat panel display devices, such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum florescent displays (VFDs) to provide necessary characteristics such as compact construction, light weight, and low power consumption. Among these flat panel devices, LCDs are extensively used due to the ease with which they are driven and their superior ability to display images.
An LCD device displays images on a screen by adjusting an amount of light being transmitted through a liquid crystal layer using refractive anisotropy. In order to display images in the LCD device, a back light (i.e., light source) is required to supply light to a liquid crystal layer of the LCD device. In general, the backlight may be divided into two types depending upon the light source (or lamp) location, namely, a lateral (side or edge) type backlight and a direct type backlight.
In the lateral type backlight, a lamp is disposed at a lateral side of the LCD panel to supply light to the liquid crystal layer, while in the direct type backlight, the lamp is disposed at a lower portion of the LCD panel to directly supply light to the liquid crystal layer. Also, the lateral type backlight is disposed at the lateral side (or edge) of the LCD panel to supply light to the liquid crystal layer through the use of a reflector and a light guide plate. Hence, the lateral type backlight can be employed in notebook computers or the like which requires thin display devices.
However, because the lamp is disposed at the lateral side of the LCD panel, it is difficult to employ a lateral side backlight to a large sized LCD panel. Moreover, it is difficult to obtain high level brightness because the light is supplied through the light guide plate. Thus, the lateral type backlight cannot be applied to an LCD panel for a large size LCD TV.
On the contrary, the direct type backlight can be applied to large LCD panels because light is directly supplied from the lamp to the liquid crystal layer, thereby obtaining high level brightness. Thus, the direct type backlight can be used for LCD TVs.
For a backlight lamp, a light emitting device that spontaneously emits light, such as a light emitting diode (LED) can be used instead of a fluorescent lamp. Such a light emitting device emits R, G and B monochromatic (i.e., single color) light. Accordingly, upon using such light emitting devices as a backlight, a high color reproduction rate can be advantageously obtained with a minimal driving (operation) power.
FIG. 1 illustrates a structure of the related art LCD device employing light emitting devices as a backlight lamp. As shown in FIG. 1, an LCD device 1 includes an LCD panel 3 and a backlight 10 installed at a rear surface of the LCD panel 3. Images can be displayed on the LCD panel 3, which includes a lower substrate 3a and an upper substrate 3b that are both made of a transparent material, such as glass, and a liquid crystal layer (not shown) interposed therebetween. Particularly, although not shown in the drawing, the lower substrate 3a is often referred to as a thin film transistor (TFT) substrate because driving devices such as thin film transistors and pixel electrodes are formed thereon. The upper substrate 3b is often referred to as be a color filter substrate because a color filter layer is formed thereon. A driving circuit unit 5 is provided at a lateral (side or edge) surface of the lower substrate 3a to apply electronic signals to the thin film transistors and the pixel electrodes formed on the lower substrate 3a. 
Further, the backlight 10 includes a plurality of light emitting devices 11, installed at a lower lateral (side or edge) surface of the LCD panel 3, that emit and provide light to the LCD panel 3, a light guide plate 15 to guide the light emitted from each of the light emitting devices 11 to the LCD panel 3, and a reflector 17 to reflect the light emitted from each of the light emitting devices 11, to thereby improve luminance efficiency.
In addition, a diffusion plate (not shown) can be provided at an upper portion of the light guide plate 15 to diffuse the light and to provide a uniform distribution of the light to the LCD panel 3.
The light emitting devices 11, which are R, G, and B light emitting devices to emit the R, G and B monochromic light, are provided in plurality at a lateral (side or edge) location of the backlight 10 with certain intervals between each light emitting device 11. The plurality of light emitting devices 11 are aligned in two or more lines (i.e., two or more rows or columns). R, G, and B monochromic (single color) light is respectively emitted from each of the R, G and B light emitting devices. Each of the R, G and B monochromic light is mixed (combined) together to form so-called white light, and thereafter the white light is supplied to the LCD panel 3 via the light guide plate 15.
However, the related art backlight having the above-described structure may have the following problems. As illustrated in FIG. 2, the light emitting devices 11 are arranged in multiple lines (e.g., only two lines shown in FIG. 2 for simplicity) at the lateral (side or edge) wall 12 of the backlight 10. Here, the R, G and B light emitting devices are mounted in sequential order. Each of the R, G and B monochromic (single color) light emitted from each of the light emitting devices 11 is directed to be incident directly onto the light guide plate 15 or upon being reflected by the reflector 17 at the lower portion thereof.
When the monochromic light emitted from each of the R, G and B light emitting devices 11 is reflected by the reflector 17, an intensity of the monochromic light particularly reflected at a portion near or adjacent to each light emitting device 11 is greater than that of other emitted or reflected light. Accordingly, all the monochromic light provided to the LCD panel 3 is not completely converted into white light due to the differences in the intensities of each type of monochromic light (i.e. R, G, B light being provided directly to and reflected to the LCD panel 3), which ultimately causes undesirable degradation in the quality of images shown on the LCD panel 3.